U.S. patent application Ser. No. 80,475, now U.S. Pat. No. 4,281,741, filed Oct. 1, 1979, the disclosure of which is hereby incorporated by reference in the present application, contains a brief dicussion of earlier uses of locomotive exhaust silencers. This discussion includes reference to a silencer used with turbocharged diesel powered domestic road type locomotives having a single elongated exhaust outlet opening upwardly from the turbine. That silencer includes a dual bend offset outlet conduit that provides broad band sound reduction in the medium and high frequency range, combined with a large tank defined expansion chamber surrounding the lower portion of the outlet conduit and connected thereto by perforations through the conduit wall, so as to provide sound reduction in the lower frequency ranges.
Upon the release of an improved diesel locomotive providing for operation of the diesel engine at higher horsepower and speed, the above-described silencer arrangement was modified in order to maintain the engine exhaust noise level below established noise standards. Modifications included the provision of a sharper bend in the offset outlet conduit and the addition of increased communication between the conduit and the associated expansion chamber. While these changes satisfactorily controlled the increased exhaust noise level of the higher horsepower engine, they also had the effect of causing a slightly increased restriction to exhaust gas flow with a resultant adverse effect upon engine fuel efficiency.
Accordingly, it was desired to provide an improved engine silencer arrangement having the capability of maintaining exhaust noise within established standards while reducing exhaust back pressure to improve fuel efficiency.